Electrolytic cell arrangement



NOV. 17, 1970 G, R, GREEN 3,540,991

ELECTROLYT I C CELL ARRANGEMENT GERALD GREEN I* 7. VENTOR. BY. waff ,M

A TTOWEYS Nov. 17, 1970 G. R. GREEN ELEGTROLYTIC CELL ARRANGEMENT 4Sheets-Sheet 2 Filed Dec. 1l, 1967 GERALD R. GREEN E; yNZENToR:

,arroRA/Ers dwf/M Nov. 17, 1970 G. R. GREEN 3,540,991

ELECTROLYTIC CELL ARRANGEMENT Filed Dec. 1l, 1967 4 Sheets-Sheet 3GERALD GREEN l INVENTOR.

A TTUR/VEYS I Nov. 17, 1970 G. R. GREEN 3,540,991

ELECTROLYTIC CELL ARRANGEMENT Filed Dec. l1, 1967 4 Sheets-Sheet 4'GERALD l?. GREEN v n INVNTOR. 8*/ @wf/4 A TTORNE'YS Sttes ate 3,540,991ELECTROLYTIC CELL ARRANGEMENT Gerald R. Green, Rochester, N.Y., assignorto Eastman Kodak Company, Rochester, N.Y., a corporation of New JerseyFiled Dec. 11, i967, Ser. No. 689,533 Int. Cl. Blilk 3/00; C22d 1/02U.S. Cl. 2424-275 2 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THEINVENTION The electrolytic refinement of various metals has generallybeen performed in electrolytic cells of either the T hum or the Moebiustype wherein the metal to be rened is suspended as an anode within atank containing the proper electrolytic solution and an electric currentis applied between the metal being refined and a cathode surface whichis spaced from the metal anode in the cell. In the Thurn cell the anodeis generally suspended horizontally in the electrolytic solution whichis contained in a shallow rectangular tank, the bottom of which formsthe cathode. In the Moebius cell, the anode and the cathode are arrangedvertically within a deeper tank, with the cathode often forming thesides of the tank.

In the operation of the foregoing electrolytic cells, the source metal,containing various impurities, is cast as an anode plate which issuspended in the electrolytic solution. Generally, the anode plate isenclosed in a canvas bag and is supported by a basket in theelectrolytic solution. The canvas bag prevents the contamination of boththe electrolytic solution and the refined metal by insoluble impuritiesas the anode plate is disintegrated by the electrolytic process.

Moebius type refining cells have heretofore been provided withmechanical scrapers to dislodge the deposited metal from the verticalcathode surfaces so that the relined metal particles fall to the bottomof the cell. However, to remove these metal particles from the bottom ofthe Moebius cell requires that the refining operation be interrupted.Thum cells have the advantage over Moebius cells of being mechanicallysimpler in construction and of permitting removal of a portion of thedeposited metal without completely interrupting the operation of thecell. However, it still has been necessary to manually remove thedeposited metal from the bottom of the Thum cell.

The manual removal of deposited metal from the bottom of the Thum andMoebius type electrolytic cells is undesirable in part because of thefact that the metals must be removed relatively frequently to preventtheir accumulation which may cause the gap between the cathode and thesource metal anode to be bridged and thus short out the cell. Moreover,manual removal of the metal requires that the operator reach into theelectrolytic solution (silver nitrate in the case of silver refining)and manually dig it out. This results in splashing and dripping of thesolution, which may be hazardous to the operator and to the equipment.Moreover, this operation generally results in the operator beingsubjected to a fume-laden atmosphere which may have harmful effects.

Usually the economics involved in manually removing the deposited metalfrom the cells has resulted in a reduction in the frequency with whichthe metal is removed. In these circumstances, in order to prevent thebuild-up of metal to the point of shorting out the cell and to provideaccess to the deposited metal, it has been necessary to constructoversized cells wherein less than half of the cell volume is used forrefining metal. As a result, the efficiency of the cell per unit volumeis considerably lower than might otherwise be possible, requiringexcessive operating floor space and volume of electrolytic solution.Furthermore, the value of the metal held in inventory in theelectrolytic cell, especially when precious metals are involved, oftensubstantially increases the cost of performing the refining operation.

Attempts have been made at overcoming the foregoing disavantages.However, due to the complexity of the apparatus and the relatively shortlifetime of the parts in the electrolytic solution, they have not beengenerally adopted. One of the major disadvantages of prior art apparatusfor automatically removing metal from electrolytic cells is the use ofmetal parts which are susceptible to electrolysis and thus requirefrequent replacement. Other apparatus utilizing materials which aresubstantially inert in the cell environment utilize rotating or othercomplex moving parts which are subject to severe wear from the fineparticles of metal in the electrolytic solution. As a result of theforegoing drawbacks, automatic removal of metal from electrolytic cellshas not gained widespread acceptance and manual removal of the metalfrom the bottom of the cell is still the common mode of operation.

Similarly, electrolytic cells employing cathodes in the form of a movingconveyor belt in the bottom of the cell have been proposed in an attemptto provide for mechanical removal of the refined metal. However, it hasbeen found that such arrangements do not provide for acceptableequipment life and the electrical connections to the moving cathodeelement make the resulting apparatus unduly complex. Moreover, it hasbeen found that such prior art arrangements have the undesirablecharacteristic of providing very uneven current densities over the areaof the cathode. Thus at some portions of the cathode the current densitymay be so low that practically no electrolysis takes place while atother locations the current density is so great that impurities are alsoplated out, resulting in incomplete metal refinement.

It is apparent that apparatus for the automatic removal of refined metalfrom electrolytic cells of the type described, which is sufficientlydependable, maintenancefree and without the foregoing disadvantageswould be extremely desirable. Not only would such an arrangementminimize the hazards to which cell operators are now exposed duringoperation of the cell, but it would also result in substantial economiesboth in the labor and the operating space required, as well as areduction in the value of metal in inventory at the bottom of the cell.This last factor would further result in a savings in the associatedinterest charges which are often assessed against such an inventory ofprecious metals.

SUMMARY OF THE INVENTION Accordingly, the present invention provides anelectrolytic cell for refining a metal comprising a tank containing anelectrolytic solution having a liquid surface. A pair of electrodes arearranged in spaced relationship in the electrolytic solution with atleast a portion of an inner surface of the tank forming the cathode. Atleast one surface in the tank slopes upward from the bottom and extendsabove the surface of the electrolytic solution. A means is arranged topull a scraper along the bottom of the tank to remove deposited metalfrom that. portion of the tank forming the cathode.

The arrangement of the present invention provides a scraper meanswherein substantially the only relative motion is between the edge ofthe scraper blade and the cathode surface whereby lifetime of the partsis substantially lengthened, making the operation economically feasible.

More specifically, a scraper assembly is provided which has a canopyplate over the scraper blade, which canopy extends a substantialdistance ahead of the leading edge of the blade. The canopy plate issupported by side plates which are closely adjacent the side of thecell. The assembly of the canopy and side plates thereby prevent themetal removed from the bottom of the cell from spilling over the top ofthe blade or piling up in front of it to the extent that it bridges thegap between the anode and the cathode and shorts out the cell.

Furthermore, the side plates of the scraper assembly may be providedwith scraper edges at either end to assist the main scraper blade inremoving the rened metal.

The present invention also provides an arrangement wherein asubstantially uniform current supply may be provided to both the anodeand the cathode.

The various features of novelty which characterize the present inventionare pointed out with particularity in the claims annexed to and forminga part of this speciication. For a better understanding of theinvention, its operating advantages and the specific objects obtained byits use, reference should be had to the accompanying drawings anddescriptive matter in which the preferred embodiments of the presentinvention are illustrated and described.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a sectional elevation viewof an electrolytic cell incorporating a specific embodiment of thepresent invention;

FIG. 2 is a section taken across the cell along line 2--2 of FIG. 1;

FIG. 3 is a perspective view, looking upward at the bottom of thescraper assembly utilized in the foregoing specic embodiment;

FIG. 4 is a sectional elevation view of an electrolytic cellincorporating an alternate embodiment of the present invention;

FIG. 5 is a sectional view of the alternate embodiment taken along line5 5 of FIG. 4; and

FIG. 6` is a perspective View of the scraper assembly used in thealternate embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT An electrolytic cell 10incorporating a specific embodiment of the present invention isillustrated in FIG. 1 and comprises an elongated tank having a bottom 12and a pair of side members 14. The cell normally contains anelectrolytic solution having a liquid surface 16 adjacent the top of thesides of the cell. At one end of the cell a portion 18 of the bottomslopes upwardly therefrom and extends above the solution surface 16. Aplurality of anode support baskets 20 are disposed in the upper portionof the cell and may be suspended from the side members 14 in a mannerwell known in the art. The support baskets each consist of a peripheralframe member 22 arranged to be supported on the top of the side members.The bottom of the support basket may be formed of a plurality of spacedbars 24 or other structure which provides the necessary support to ananode plate 26 while permitting the electrolytic solution to come intocontact with it. While the cell may be arranged with only one continuousbasket extending throughout the length of the cell, it has been found tobe more advantageous to provide a plurality of similar separate basketsin side 4 by .side relationship to permit easier handling ofthe baskets.

In the cell illustrated, the bottom 12 is. formed of stainless steelwhich forms the cathode of the cell. Bus.

bars 28, formed of copper bars, are attached to the bottom or exteriorof the cathode by a `plurality of clamps 30, which also join the bottom12 with the anges 32 of the side members 14. The bus bars assure thatthe cathode will receive a substantially uniform supply of currentthroughout the cell. The anode 26 of the cell is formed of a pluralityof plates of the metal being refined which may be cast with an integralrib 34 on the top surface thereof. The anode current connection isprovided by a mechanical clamp 36 which is removably attached to the rib34. The anode plate is normally disposed in a cloth bag 38 to preventthe introduction of impurities into the refined metal at the bottom ofthe cell. The anode plate and the enclosing cloth bag are then supportedin a basket 20 so that at least the lower surface of the anode issubmerged in the electrolytic solution.

A scraper assembly 40 is disposed in the bottom Vof the cell and ismovable longitudinally along the cell. The scraper assembly comprises acanopy which is formed of a stationary horizontal plate member 42 whichextends across the cell and is supported from the bottom of the cell bya pair of side members or plates 44. A scraper blade y46 is disposedbetween the side plates at one end thereof beneath the canopy plate. Thescraper blade 46 may be pivotally supported by the side plates 44 andhas a lower edge which is arranged to engage the upper surface of thebottom or cathode 12 of the cell. The lower scraping edge of the blademay be provided with a plastic tip 48 to minimize the possibility ofdamage to the smooth surface of the cathode. Each end of the side plates44 is provided with a scraper-like blade 50 to remove any depositedmetal from the intersection of the cathode 12 and the side members 14 ofthe cell. A cable 52, preferably formed of a plastic material inert inthe electrolytic solution, is connected to the top of the leading edgeof the scraper blade 46, and extends horizontally along the cell to theend thereof provided with the upward sloping bottom portion 18 which maybe part of the cathode 12 or a non-conducting extension thereof. Thecable extends upward to a drive motor 53 which, when activated, pullsthe blade assembly along the bottom of the cell scraping any depositedmetal from the cathode and eventually pushing it up the sloping bottomportion 18 of the cell and into a receptacle 54 exterior of the cell.Means is provided for returning the blade to the opposite end of thecell to repeat the scraping operation. In the embodiment illustrated,the cable extends from the drive motor above the cell to the oppositeend where it re-enters the solution and is connected to the oppositeside of the scraper blade 46. In the present arrangement, the blade ispivoted so that it provides little or no scraping action as it is drawnback to the starting point. However, it will be readily apparent thatboth ends of the electrolytic cell may be provided with an upwardsloping bottom portion and an associated metal receptacle so that thescraper blade could remove metal While traveling in either direction. Insuch an arrangement the scraper blade could be fixed in position and thecanopy blade would extend substantially equi-distant on either side ofthe blade.

The leading and trailing ends of the canopy blade may be provided with atriangular tongue blad'e 56 which is provided with a guide cleat 58 thatengages the cable 52 extending from the scraper blade 46. Thisarrangement assists in guiding the scraper assembly and maintaining itsalignment in the cell throughout its travel. Moreover, a bearing means,such as rollers 60 and y62, may be provided at each end of the cell toguide the cable 52 as it travels upward out of the electrolyticsolution.

The scraper assembly ,is preferably formed of stainless steel encased ina plastic material Which is inert in the electrolytic solution. Thestainless steel provides suflicient weight to the assemblyto prevent itfrom oating in the solution and thereby not completely removing thedeposited metal from the cathode plate. Except for the stainless steelcathode bottom and the source metal anode plates, the remainder of thecell structure in contact with the electrolytic solution may be formedeither of a plastic material or of plastic-encased metal parts.

Normally, a Ventilating hood 64 is disposed over the top of the cell toremove any fumes generated thereby. Access doors may be provided inthehood to permit the ready addition of new anode plates.

In operation, the cell is lled with a suitable electrolytic solutionsubstantially to the top of the side members 14, and a plurality ofanode plates of the source metal, encased in a cloth bag, are supportedin the basket with at least a portion of the plates being submerged` inthe electrolytic solution. Each of the anode plates is connected by aclamp 36 to an electric lead 66 from a suitable source of electriccurrent, the opposite side of which is substantially permanentlyconnected to the cathode 12 through the bus bars 2S. The current llow isinitiated and the metal of the anode plate is electrolyzed and isdeposited onto the surface of the cathode. Simultaneously with thecommencement of current flow through the cell, the scraper assemblydrive motor 53 is started, pulling the scraper assembly 40 along thebottom of the cell. The scraper blade removes any metal which has beendeposited on the cathode and pushes it ahead'. rPhe canopy plate 42 andside plates 44 guide the collected metal and prevent it from beingwashed over or around the scraper blade 46. Furthermore, the canopyplate prevents the metal from building up to the extent that it mightshort out the cell.

As the scraper assembly reaches the upward sloping portion of thebottom, the metal is moved up and out of the electrolytic solution andis nally pushed over the edge of the cell into the collectionreceptacle. A limit switch may be provided to stop the drive motor whenthe scraper assembly reaches the uppermost end of the sloping portion ofthe cell. At that time, the drive motor is reversed and the scraperassembly is returned to the starting end of the cell where it againreverses direction and repeats the scraping operation.

It will be appreciated that while the specific embodiment illustrated isarranged such that the Scraper blade removes metal during travel in onlyone direction, a cell arrangement can be employed wherein metal removaltakes place during scraper travel in either direction. While the presentcell arrangement is shown with one end thereof sloping upward from thebottom, it is possible that either of the sides of the cell couldlikewise slope outwardly toward the top whereby the scraper assemblywould extend throughout the length of the cell and would be arranged tomove across it. However, it 'has been found most economical to constructsuch cells with a length substantially greater than the width so thatthe end of the cell is the most practical location at which to removethe rened metal.

An alternate embodiment of the present invention is illustrated in FIGS.4, 5, and 6 wherein an electrolytic cell of the Moebius type is arrangedfor automatic removal of the re'ined metal. In this arrangement, theanode plates 70 are suspended substantially vertically within a deepcell with all of the cell tank walls 72 forming the cathode surface. Inthis arrangement it is necessary to provide a scraper assembly 74 whichextends across the bottom of the cell and up the adjacent sides toremove any metal deposited on all three surfaces. As shown in FIGS. 4and 6 the scraper assembly 74 of this arrangement is provided with acanopy 76 which also extends upwardly along the Vertical portion of thescraper blade 78 to prevent the metal being removed from the cathode 72from piling against the anode plates 70 and shorting out the cell. Thealternate embodiment illustrated is arranged for removal of the refinedmetal from either end so that the scraper blades may be stationary.Otherwise, the operation of this alternate embodiment is substantiallythe same as that described with respect to the preferred embodiment.

Accordingly, it will be seen that the present invention provides anarrangement for continuously removing refined metal from an electrolyticcell which is both of simple construction and economical operation andwhich also permits improved operating eiciencies in the cell itself. Atthe same time, the present invention substantially eliminates thehazards to the operator attendant in the manual cleaning procedures ofthe prior art. Moreover, the amount of operating space necessary for theoperation of the electrolytic cell incorporating the present inventionis substantially reduced with the attendant economies. Furthermore, theamount of metal retained in the cell between removal operations isgreatly reduced, resulting in a substantial reduction in inventorycosts. The present invention similarly provides a scraper arrangementwhich simply and efficiently removes the refined metal without thepossibility of shorting out the cell. In addition, the construction issimple and rugged, reducing the maintenance required and extending theoperating life thereof.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will lbe understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinabove and as defined in the appendedclaims.

I claim:

1. An electrolytic cell for the refinement of a metal comprising a tankarranged to contain an electrolytic solution having a liquid leveltherein, a plurality of anode plate support baskets arranged in saidtank with at least a portion thereof below the liquid level of theelectrolytic solution, a metal cathode plate having an exposed uppersurface in contact with said electrolytic solution and forming thebottom of said tank, a bus bar extending along and connected to thebottom surface of said cathode plate, means for connecting said cathodeplate to a source of electric current, one end of said cathode platearranged to slope upwardly and outwardly therefrom and to extend abovethe level of the electrolytic solution, a scraper assembly arranged formovement longitudinally along said tank and supported by the cathodeplate, said scraper assembly comprising a pair of side members disposedadjacent the sides of said tank, a canopy plate extending between saidside members above the cathode plate and below said support basket, ascraper blade supported by and between said side members beneath saidcanopy plate, said scraper blade having a lower scraping edge arrangedto engage the upper surface of said cathode plate, cable means connectedto the scraper assembly and extending in Iboth directions substantiallyperpendicular thereto, and means for driving said cable means to movesaid scraper assembly along the cathode plate and up the sloping portionthereof to remove metal deposited on the cathode plate from saidelectrolytic solution.

2. An electrolytic cell for the renement of a metal comprising a tankarranged to contain an electrolytic solution having a liquid leveltherein, a plurality of plate support baskets arranged in said tank withat least a portion thereof in said electrolytic solution, a plurality ofanode plates supported in said support baskets in contact with saidelectrolytic solution, a metal cathode plate having an exposed uppersurface in contact with said electrolytic solution and forming thebottom of said tank, a bus bar extending along and connected to thebottom surface of said cathode plate, means for connecting said anodeplates and said cathode plate to a source of electric current, one endof said cathode plate arranged to slope upwardly and outwardly therefromand to extend above the level of the electrolytic solution, a scraperassembly arranged for movement longitudinally along said tank andsupported by the cathode plate, said scraper assembly comprising a pairof side members disposed adjacent the sides of said tank, a canopy plateextending between Said side members above the cathode plate and belowsaid support basket, a scraper blade supported by and between said sidemembers beneath said canopy plate, said scraper blade being disposedsubstantially at one end of said side members, said scraper blade havinga lower scraping edge arranged to engage the upper surface of saidcathode plate, said blade being pivotally supported by said members,cable means connected to the top edge of said scraper blade andextending in both directions substantially perpendicular thereto, andmeans for driving said cable means to move said scraper assembly alongthe cathode plate and up the sloping portion thereof to remove metaldeposited on the cathode plate from said electrolytic solution.

References Cited UNITED STATES PATENTS 579,236 3/1897 Kellner 204-212616,891 1/1899 Burton 204-275 X 693,678 2/1902 Wilson 204275 X 922,4705/1909 Gilchrist et al. 204-287 1,124,315 l/1915 Michaud et al. 204-275X 2,558,750 7/1951 Harrison 204l0 X HOWARD S. WILLIAMS, Primary ExaminerA. C. PRESCOTT, Assistant Examiner

